Narrow Spectrum-penicillins

Question 1

What are common indications?

Answer 1

Bnexylpenicillin/phenoxymethylpenicillin;

Strep infections
Meningococcal disease

Penicillinase-resistant penicillin - flucloaxacillin

Staphylococcus infections

Question 2

Give examples of streptococcal infections? What narrow spectrum penicillin is active against it?

Answer 2

Tonsilitis
Penumonia
Endocarditis

Benzylpenicillin
Phenoxymenthylpenicillin

Question 3

Give examples of meningococcal infections.

What abx is active against it?

Answer 3

Meningitis

Benzylpenicillin
Phenoxymenthylpenicillin
Though cephalosporins are preferred in hospital settings

Question 4

What are examples of staph infections and what can be used against it?

Answer 4

Skin
Bone
Soft tissue
Bone and joint infections
Otitis externa
Endocarditis

Flucloxacillin

Question 5

What is the spectrum of activity of flucloaxacillin that differs from other penicillins?

Answer 5

It contains an acyl side chain
Which protects the Beta lactam ring ( needed for bacteriacidal activity)

Effective against Beta lactamase produced by staphyloccoci

Question 6

How does MRSA confer resistance of flucloxacillin?

Answer 6

By changing its target enzymes to reduce penicillin binding affinity

Question 7

What are side effects of narrow spectrum?

Answer 7

Neurological toxicity (including convulsions and coma) at high doses due to accumulation

Rare- liver toxicity

Question 8

Who should be prescribed with caution?

Answer 8

Dose reduced in severe renal impairment

Question 9

What are doses for severe infections?

Answer 9

Severe:IV
Benzylpenicillin 1.2g every 4-6 hours

Flucloaxcilliin: 1-2g 6 hourly

Question 10

Why should penicillins IV be given frequently?

Answer 10

Penicillins are rapidly excreted by kidney

Have a short half life

Adminstered frequently to maintain therapeutic plasma levels.

Question 11

When would a prolonged course of IV be needed?

Answer 11

High dose IV needed for deep seated infections such as osteomyelitis and endocarditis

Question 12

Why is phenoxymethylpenicllin not used for severe infections

Answer 12

As it is less effective than other narrow spectrum penicillins ( Benzylpenicillin) and GI absorption is unpredictable

Question 13

What are dosages for less severe infections?

Answer 13

Flucloxacillin- 250-500mgQDS

Phenoxymethylpenicillin-

500mg QDS